H.W. Colvin

Bloat in sheep (Ovis aries)

1. Most of the field studies on bloat are conducted with cattle and most of the laboratory experiments seeking to explain the various parameters associated with bloat are done with sheep. 2. Based on grazing behaviour, it would be expected that sheep might bloat more severely than cattle because they selectively choose to eat leaves over stems and chew what they ingest more frequently than cattle. Furthermore, sheep appear to select legumes over grasses because the legumes can be eaten more rapidly. However, because they are selective, sheep eat more slowly than cattle. Despite a higher bloat expectation, bloating in sheep is reported to be less of a problem than in cattle. 3. Although frothing of rumen ingesta was described earlier in cattle as the cause of acute legume bloat, experiments with frothy bloat in sheep preceded those in cattle. 4. Anti-frothing agents were used in sheep before cattle to treat acute legume bloat. 5. Experiments devoted to the study of eructation in ruminants were carried out on sheep, then cattle. 6. Convincing evidence that rumen motility does not cease during acute legume bloat was gathered using sheep. 7. Although the transected tracheal technique for the determination of the volume of eructated gas was developed with cattle, the pathway of eructated gas was confirmed with sheep. 8. All the current evidence accumulated from experiments with sheep supports the hypothesis that death due to legume bloat is caused by acute neural, respiratory, and cardiovascular insult resulting from the effect of the distended rumen on thoracic viscera, diaphragm, intercostal muscles, and the abdominal vena cava. 9. Experiments with sheep and cattle being fed scabrous and nonscabrous diets similar in chemical composition show that sheep are more resistant than cattle to the increase in intrarumen pressure, decline in rumen contraction amplitude, and decrease in rumen contraction frequency caused by nonscabrous diets. 10. The sequence of events in the reticulorumen during primary and secondary contractions previously described following visual and palpation experiments with cattle was confirmed by the use of myoelectrodes implanted in the various sacs of the reticulorumen of sheep. 11. Elevated intrarumen pressure is associated with an increase in the frequency of primary (mixing) and secondary (eructation) contractions (more secondaries than primaries).(ABSTRACT TRUNCATED AT 400 WORDS)

Elevated intra-rumen pressure and secondary rumen contractions in sheep (Ovis aries)

1. Sheep rumens were insufflated with nitrogen to 5, 10, 15, and 20 cm water pressure and sustained at each pressure for 10 min. 2. Measurements included rumen motility, reticulorumen myoelectric activity, eructation frequency and volume, changes in tracheal pressure and rumen contraction amplitude. 3. As intra-rumen pressure increased, contractions designated as special secondary contractions appeared. 4. At a pressure of approximately 15 cm water, most of the special secondary contractions became regular secondaries; therefore, the special secondaries were called pro-secondary contractions. 5. Increased intra-rumen pressure was associated with respiratory distress. The recovery phase following, rumen insufflation was accompanied by hyperpnea.

The primary-secondary rumen contraction and gas expulsion in sheep (Ovis Aries)

1. Sheep rumens were insufflated with nitrogen to 5, 10, 15 and 20 cm HOH pressure and sustained at each pressure for 5 min. 2. Measurements included rumen motility, reticulorumen myoelectrical activity, eructation frequency and volume, and changes in tracheal pressure. 3. Associated with elevated intrarumen pressure was a previously unreported type of rumen contraction on which gas expulsion occurred, the primary-secondary contraction. 4. Gas expulsion volume was similar on primary-secondary and secondary contractions. 5. The maximum rumen contraction rate per min was 4-5 for secondaries and 1-2 for primary-secondaries. 6. Irrespective of the sustained initial pressure, resting intrarumen pressure was reached within 5 min.

The effect of elevation of intrarumen pressure by nitrogen insufflation on eructation in cattle (Bos taurus).

1. The intrarumen pressure (IRP) of eight calves was elevated for 10 min by nitrogen insufflation to pressures of 5, 10, 15 and 20 cm H2O. 2. Rumen motility was evaluated by recording reticulorumen myoelectrical activity and changes in luminal pressure, while eructation was determined from anterior tracheal and face mask gas expulsion. 3. The elevation of IRP increased primary rumen contraction frequency slightly and secondary rumen contraction frequency as much as 3-fold. 4. Rumen gas was expelled only during rumen contractions and virtually always during secondary rumen contractions. 5. Cattle do not exhibit the primary-secondary contraction previously identified in sheep and their rumen motility appears to be less sensitive than sheep to increases in IRP.

Vagal stimulation of gastric secretion in Gallus domesticus

Abstract 1. 1. The proventriculi of White Leghorn cocks were acutely cannulated under sodium pentobarbital anesthesia. 2. 2. Electrical stimulation of the cervical vagi was found to be a potent stimulus for both acid and pepsin secretion. 3. 3. The threshold for vagal stimulation was found to be quite high (approximately 20 V), implying a very small fiber diameter for the nerves innervating the proventriculus. 4. 4. Peak outputs of acid and pepsin in response to vagal stimulation were 0·96 ± 0·05 m-equiv. H + /30 min and 103,500 ± 19,600 P.U./30 min, respectively. 5. 5. Ganglionic blockade with hexamethonium during continuous vagal stimulation inhibited both acid and pepsin secretion equally.